Currently, one of the fastest communication data rates specified by the IEEE over structured copper cabling is 10 gigabit/second (Gbps) per the IEEE802.3ba standard. The structured cabling infrastructure called out in this standard is based on twisted pair cabling and RJ45 connectivity. This type of structured copper cabling specified by the IEEE includes four balanced differential pairs over which the Ethernet communication takes place. Compliant channels will also meet the TIA568 Category 6A (CAT6A) specifications for cable, connectors, and channels. These CAT6A components and channels provide 500 MHz of bandwidth for data communication across 100 meter links.
In June 2010, the IEEE ratified a new standard, IEEE802.3an, for high speed Ethernet communication at speeds of 40 Gbps and 100 Gbps. This new standard called for both fiber and copper media; however, the only copper media supported was a short (7m) twin-ax based copper cable assembly. No provisions were made for twisted pair structured copper links.
The traditional benefits that come with structured copper channels such as lower cost, backwards compatibility, and field terminable connectivity, are still desirable at higher speeds such as 40 and 100 Gbps. This has prompted many in the industry to investigate the feasibility of transmitting 40 Gbps over a structured copper channel. Some have speculated that higher bandwidth (1000 MHz) Category 7a (CAT7A) cables and connectivity can support 40 Gbps transmission. To achieve 1000 MHz of bandwidth in a mated connector, a fundamental change in architecture is required. Traditional RJ45 connectivity presents four pairs of contacts arranged in a parallel 1-8 in-line fashion with one pair split around another pair. With this arrangement of conductors, substantial technical challenges related to crosstalk, mode conversion, and return loss arise when the bandwidth is extended to 1000 MHz. Two different CAT7A solutions to these connectivity challenges have been accepted in the industry.
The IEC 61076-3-104 specification details one architecture that isolates the 4 pairs of contacts into individual shielded “quadrants” which allows for a more manageable approach to minimizing crosstalk and mode conversion at 1000 MHz. A fundamental drawback to at least one type of this design can be that it sacrifices one key benefit of structured copper cabling, backward compatibility, as RJ45 plugs are not compatible with 61076-3-104 type connectors.
Another connectivity solution specified in IEC 60603-7-71 incorporates two “modes” of operation to allow for backward compatibility with RJ45 style plugs, and a higher bandwidth style plug, sometimes referred to as “ARJ45”, with 4 pairs of contacts isolated in “quadrants”. An IEC 60603-7-71 type of connector design is much more electrically and mechanically challenging than the 61076-3-104 style connector, but it does maintain the key feature of backward compatibility. When mated with an RJ45 plug, the connector must provide the necessary electrical crosstalk compensation to comply with the RJ45 rated standard such as CAT6A. When mated with a 60603-7-71 plug, the connector must provide the corresponding isolated contact locations. The dual mode functionality is achieved by sharing the two outermost pairs of RJ45 contacts, grounding the middle two pairs of RJ45 contacts, and providing two new pairs of isolated contacts. In total there are six pairs of contacts in the connector, four of which are used depending on which style plug it is mated with. The presence of these extra pairs and the mechanical flexibility of the connector results in a very challenging electrical design due to potential parasitic coupling between unused contacts and/or unwanted compensation circuitry. By sharing the two outermost pairs of RJ45 contacts, any crosstalk compensation circuitry between these pairs and the other pairs can cause an unintended imbalance leading to mode conversion and increased insertion loss through the connector when mated with a 60603-7-71 plug. Conversely, when mated with an RJ45 plug, the unused isolated contacts can provide an unintended parasitic coupling path between pairs leading to degraded crosstalk, and return loss performance.
While both CAT7A connectors previously discussed support a channel with a bandwidth of 1000 MHz, capacity analysis has shown that the channel with the previously discussed connectors can only support 40 Gbps transmission over a length of roughly 25 meters. In addition, the complexity of the electronics required to transmit and receive data is significant and may not be available at a reasonable power level for 10 years or more. A higher bandwidth channel is needed to extend the reach of a structured copper channel to a meaningful distance of 50 meters. Capacity analysis indicates that the channel bandwidth will need to approach 2 GHz to optimally support 40 Gbps transmission. In addition, improved connector crosstalk and return loss performance may be required to alleviate some of the digital signal processing burden placed on the electronics, which drives the complexity and overall power consumption of the electronics.
What is needed in the art is a higher category cable and connectivity solution that supports at least 40 Gbps transmission across a structured copper channel, and which includes backward compatibility with RJ45 connectivity.